Device for igniting a combustible material



Dec. 12, 1967 w c 55 ET AL 3,357,190

DEVICE FOR IGNITING A COMBUSTIBLE MATERIAL Filed July'28, 1965 2 Sheets-Sheet l INVENTORS J. J. SCHWARTZ H.W. D. CASSIDY J. P. KING BY 5M OM ATTORNEY Dec. 12, 1967 H. w. D. CASSIDY El AL DEVICE FOR IGNITING A COMBUSTIBLE MATERIAL Filed July 28, 1965 2 Sheets-Sheet 2 lNV ENTORS J. J. SCHWARTZ H. W. D. CASSIDY J. P. KING BY @WO. W

ATTORN v 3,357,190 DEVICE FOR IGNITING A COMBUSTIBLE MATERIAL Herbert W. D. Cassidy, and John Paul King, Elkton, Md

and Jules .I. Schwartz, Wilmington, DeL, assignors to Thiokol Chemical Corporation, Bristol, Pa., a corporation of Delaware Filed July 28, 1965, Ser. No. 475,419 4 Claims. (Cl. 60-25'6) This invention relates to an ignition device, and more particularly, to an ignition device that can advantageously be used to ignite a solid propellant rocket motor.

Ignition devices used to ignite the combustible grain of a solid propellant rocket motor generally include an initiator comprising a squib that contains a comparatively small amount of a primer material that can readily be ignited at a predetermined time, as by means of an electric current passed through a bridgewire embedded in the primer material, and also a larger amount of so-called booster charge that is ignited by the primer material and in turn ignites the grain of the rocket motor. In some cases, more than one deflagrating material is ignited by the primer of an ignition device before the grain of the rocket motor is ignited, as, for example, in igniters having a primer, a first booster material in granular form disposed adjacent the primer, and a second booster material in pelletized form disposed adjacent the first booster material. To facilitate attachment of an igniter to a rocket motor, the aforementioned materials have been heretofore packaged in containers of various types, including frangible shells made of plastic, paper or metallic materials, and also in cloth bags which are often used in conjunction with containers of the aforementioned types.

Igniters which have previously been used for igniting the grain of solid propellant rocket motors have not been entirely satisfactory for various reasons. For example, igniters which utilize a solid container for holding the deflagrating materials thereof have caused malfunction of a solid propellant rocket motor as a result of fragments of the igniter container lodging in the orifice of the nozzle of the rocket motor when the igniter is fired. On the other hand, known igniters in which a deflagrating component thereof is not enclosed in a solid container, such as igniters which utilize the aforementioned cloth bag, have been found disadvantageous because of, for example, the lack of protection of the deflagrating material held in the cloth bag from damage resulting from mechanical shock or exposure to harmful gases in the environment in which the igniters are stored before they are used. Furthermore, igniters of the prior art have generally been found inadequate with respect to the manner in which the high temperature gases discharged from the primer of the igniter have been propagated over the surfaces of deflagrating materials that constitute the booster charge of the igniter.

It is, therefore, a broad object of this invention to provide an igniter which avoids the aforementioned disadvantages associated with the use of previously available igniters.

It is a particular object of this invention to provide an igniter, the housing of which effectively protects the deflagrating materials thereof and which does not fragment when the igniter is used.

It is another object of this invention to provide an igniter including inexpensive yet effective means for controlling the manner in which high temperature gases discharged therefrom are propagated.

Other objects and advantages of this invention will become manifest in the following description of two embodi- United States Patent ice ments of the invention, which are to be considered in conjunction with the accompanying drawings, wherein:

FIGURE 1 is a longitudinal sectional view of the preferred embodiment of the invention, illustrated in an operative position on the aft end of a rocket motor casing;

FIGURE 2 is a cross-sectional view of the preferred embodiment of the invention, taken along a plane represented by line 2-2 in FIGURE 1; and,

FIGURE 3 is a longitudinal sectional view of a second embodiment of the invention, illustrated in an operative position on the aft end of a rocket motor casing.

Throughout the specification and drawings, like reference numbers refer to like parts.

In FIGURES 1 and 2, an igniter constituting a preferred embodiment of this invention is illustrated in partially sectional and partially fragmentary form, the igniter comprising a housing 10 that is positioned within the orifice of a thrust nozzle 12 fixedly secured to the end closure 14 of a rocket motor casing 16. Bonded to casing 16 by means of a liner bond material 18 is a grain 2.0 of solid propellant, the aft end surface 22 of said grain being spaced from the inner surface of end closure 14. Housing 10 is bonded to thrust nozzle 12 by means of a potting compound 24 which permits the housing to be blown out of the nozzle when gas pressure within casing 16 reaches a predetermined level. A deflagrating material 30 is disposed within the interior of housing 10, the granules of this material being bonded together by means of a combustible binder to form a coherent body the aft end of which contacts a deflagrating primer material 32 cast Within the aft portion of housing 10. Electrical leads 36a, 36b extend through the end wall of housing 10 and into primer material 32, a bridgewire 38 connecting the ends of said leads. The components of the preferred embodiment which have been described at this point form what is referred to as an initiator in the claims appended hereto.

Disposed within the space between the end surface 22 of grain 20 and the inner surface of end closure 14 is a gas-impermeable, elastic bag, generally designated by the number 40, comprising a first portion 42 or neck which extends through the throat of thrust nozzle 12 and which is frictionally engaged with the outer surface of a tubular outlet 43 that projects forwardly from the forward portion of housing 10, and a second portion 44 which abuts the surface of said nozzle forward of the throat thereof. A plurality of combustible pellets 48 are confined within bag 40 so that they cannot move relative to one another. More specifically, pellets 48 are loaded into bag 40' to place the wall thereof under slight tension and cause the second portion 44 of the bag to firmly abut the surface of thrust nozzle 12 forward of the throat thereof. Potting compound 24 can be placed between housing 10 and thrust nozzle 12 after pellets 48 are loaded into bag 40.

In the preferred embodiment of the invention, housing 10 is made of paper, and is bonded to thrust nozzle 12 by means of elastomeric potting compound. Primer material 32 and deflagrating material 30 may comprise any of the many materials that are well known to persons skilled in the art of pyrotechnics, such as, for example, black powder or lead azide. Pellets 48, which have a diameter of about 0.1" and a thickness of about 0.1", comprise boron potassium nitrate. Bag 40 is formed of elastomeric material having a thickness of about 0.01, through the thickness of the bag may vary according to the heat and pressure developed therein. Commercially available latex has been found to be a suitable material for bag 40, but many other elastomeric materials which are gas-impermeable, elastic and combustible may also be used. Electrical leads 36a, 36b and bridgewire 38 are comprised of conventional materials. It is to be clearly understood, however, that the invention is not limited to the specific materials that have been mentioned, as many other materials that are well known to those skilled in the art of igniter design and construct-ion may be substituted for the given materials. For example, housing may, in some applications of the invention, be formed of metal foil. The invention is not limited with respect .to the particle size of defiag-rating material that is confined within bag 40, and in some instances, it may be preferable to replace pellets 48 with a deflagrating material in another form.

When the described initiator is actuated by means of electric current passed through electrical leads 36a, 36b and bridgewire 38, primer 32 and defiagrating material 30 are in turn ignited, and the high temperature .gas generated by combustion of these materials is discharged through outlet 28 into bag 40. It has been found that bag 40... is not. immediately ruptured by the gas discharged therein, but instead is expanded by this gas and eventuality ruptures. Since the volume of bag 40 increases while pellets 48 are being ignited by the hot gas discharged from outlet 28,, the pressure within the bag does not rise as rapidly as, or to the level of, the pressure in igniters wherein deflagrating materials are enclosed in rigid containers. In contrast to the manner of operation of igniters in which deflagrating materials are held in cloth bags, gas discharged into bag 40 :cannot immediately pass through the wall thereof, and consequently as the volume of said bag increases, the pellets 48 confined therein are fluidized by said gas, i.e., the closely packed pellets are separated from one another and surrounded by the high temperature gas discharged into bag 40 as the latter expands. The period of contact between pellets '48 and the gas discharged into bag 40 is comparatively long as the pellets are confined within the bag until it ruptures, whereas in some of the igniters heretofore employed, gas generated by the primer materials tends to blow secondary ,deflagrat-ing materials away from the primer gas discharge outlet and the period of contact between such secondary defiagrating materials and the primer gases is consequently limited.

Confinement of pellets 48 within bag .40 under tension, with the second portion 44 of said bag being firmly held against the surface of thrust nozzle 12 forward of the throat thereof, as has been described hereinbefore, precludes powdering or breakage of the pellets such as can occur when ignition devices in which deflagrating materials are not immobilized are subjected to vibration. Since bag 40 is formed of gas impermeable material, it also protects pellets 48 from moisture or contaminating gases. The elastomeric material of which bag 40 is made burns rapidly and completely in casing 16, and does not pass through thrust nozzle 12 in the form of pieces which would block its orifice. When the bag ruptures, the high temperature gas accumulated therein Will be propagated in a predetermined direction. Thus in the case of the preferred embodiment, bag 40 is shaped so that it top tures at a point thereon remote from the orifice of thrust nozzle 12, with the hot gas escaping from the bag in a direction generally radial to said orifice. Hence, the construction and arrangement of the preferred embodiment of the invention provides for propagation of high temperature ignition gas in a direction generally parallel to the end surface 22 of grain 20, whereas if the housing of a conventional igniter were mounted in the orifice of thrust nozzle 12, gas discharged therefrom would initially travel in a direction generally parallel to the longitudinal axis of casing 16 and perpendicular to said end surface 22.

In FIGURE 3 is illustrated a second embodiment of the invention comprising a housing 110 containing an ignition mixture 132 that can be ignited by electric current passed through electrical leads 136a, 1361; connected to a bridgewire 138. Each of the electrical leads passes through a hole in a seal disk 50 removably positioned within a thrust nozzle 112 that is fixedly attached to the end closure 114 of rocket motor casing 116. The end of a gas-impermeable, elastic bag 140, formed of an elastomeric material and filled with a defiagrating material 148, is fixedly secured to housing by means of pressure sensitive plastic tape 52. If desired, housing 110 can be attached to casing 116 or end closure 114 by suitable means to prevent shifting thereof.

The components of the second embodiment of the invention may be made of the same materials that have been mentioned in connection with corresponding components of the above-described preferred embodiment of the invention. It will be readily understood that the construction and arrangement of the second embodiment of the invention provide the same advantages that are obtained by means of the preferred embodiment of the invention, which have been noted in the foregoing description thereof. Thus when electric current is passed through electrical leads 136a, 136b, the gas of combustion of ignition mixture 132 discharges through outlet 1430f housing 110 into bag 14.0, igniting the deflagrating material 148. Bag 140 expands and eventually ruptures, at which time the end surface 122 of the solid propellant grain 120 .in rocket motor casing 116 is ignited and seal disk 50 is blown out of thrust nozzle 1 12. An advantage of the sec- 0nd embodiment of the invention is that the igniter housing and ,bag assemb y can be positioned adjacent any .selected portion .of the end surface 122 of the grain of a rocket motor, and, if desired, a plurality .of igniter assemblies of the type illustrated in FIGURE 3 and described immediately hereinabove can be placed at different points relative to the surface of a solid propellant grain of large diameter and simultaneously ignited. Preferably the largest dimension of housing 110 of the second embodiment of the invention is smaller than the diameter of the orifice of thrust nozzle 112 and the housing is made of paper or other combustible material that will be completely burned by the high temperature gas generated by combustion-of grain 120.

It will :be understood that the size of the components of the preferred embodiment of the invention will depend upon the-size of particular rocket motors with which the ignition device is usedpMoreover, although the invention has been described and illustrated with reference to use in rocket motors, the utility of the invention is obviously not limited .to such use, since its advantages may be applied to the ignition of :many deiferent kinds of gas generators, explosives or other pyrotechnic devices. It will also be obvious that various changes can be made in the materials and construction of the preferred embodiment, which have been described for the purpose of illustration and example only and not by way of limitation, without departing from the principles of the invention, the scope .of which is to be'limited only by the terms of the subioined claims.

What is claimed is:

1. An ignition device comprising:

an initiator adapted to discharge a high temperature gas from an outlet thereof at a predetermined time;

a gas impermeable inflatable bag fixedly secured to said initiator so that said gas discharged from said outlet is received therein;

a defiagrating material confined within said bag and adapted to be ignited by said gas discharged from said initiator; and

means for actuating said initiator, whereafter gas from said initiator is discharged into and inflates said bag, said deflagrating material is ignited by said gas from said initiator, and said bag is ruptured after being inflated to a predetermined limit.

2. in a rocket motor having a casing, a solid propellant grain disposed within said casing, and a thrust nozzle mounted on said casing, ignition apparatus comprising:

an initiator adapted to discharge a high temperature gas from an outlet thereof when actuated;

a gas impermeable, inflatable bag disposed within said casing adjacent said grain and fixedly secured to said initiator so that said gas discharged from said outlet is received therein;

a deflagrating material confined within said bag and means for actuating said initiator, whereafter gas from said initiator is discharged into and inflates said bag, said deflagrating material is ignited by said gas from said initiator, said bag is ruptured after being inflated to a predetermined limit, and said grain is ignited by gas generated by combustion of said deflagrating a defiagrat-ing material confined within said bag and adapted to be ignited by said gas discharged from said initiator; and

means for igniting said deflagrating material disposed within said housing, whereafter gas from said initiator is discharged into and inflates said bag, said deflagrating material confined within said bag is ignited by said gas from said initiator, said bag is ruptured after being inflated to a predetermined limit, and said grain is ignited by gas generated by combustion of material. 10 3. In a rocket motor having a casing, a solid propellant grain disposed within said casing, and a thrust nozzle 4. Apparatus as defined in claim 3 wherein said deflamounted on said casing, ignition apparatus comprising: grating material confined within said bag is in pelletized an initiator including a housing removably mounted form.

within the orifice of said thrust nozzle and a defla- 1 grating material disposed within said housing and adapted to generate a high temperature gas when said deflagrating material confined within said bag.

References Cited UNITED STATES PATENTS ignited, said housing having an outlet for said gas 2,561,670 7/1951 Miller et a1 102 49 at the forward portion thereof; 2,828,692 4/1958 Webster 60--39.82 X a gas impermeable, inflatable bag having a first portion 20 3038302 6/1962 Thalckrey 60 39'82 X thereof fixedly secured to said housing so that gas g;

discharged from said outlet is received therein, and a second portion thereof that abuts the surface of said thrust nozzle forward of the throat thereof; CARLTON CROYLE Primary Examiner 

1. AN IGNITION DEVICE COMPRISING: AN INITIATOR ADAPTED TO DISCHARGE A HIGH TEMPERATURE GAS FROM AN OUTLET THEREOF AT A PREDETERMINED TIME: A GAS IMPERMEABLE INFLATABLE BAG FIXEDLY SECURED TO SAID INITIATOR SO THAT SAID GAS DISCHARGED FROM SAID OUTLET IS RECEIVED THEREIN; A DEFLAGRATING MATERIAL CONFINED WITHIN SAID BAG AND ADAPTED TO BE IGNITED BY SAID GAS DISCHARGED FROM SAID INITIATOR; AND 